Golf ball

ABSTRACT

In a golf ball having a core and a cover of at least one layer, the outermost layer of the cover is formed of a resin composition that includes (A) 100 parts by weight of a thermoplastic resin, and (B) 1 to 30 parts by weight of a compound having a fluorene skeleton, or a derivative thereof, and the resin composition has a melt flow rate of at least 3.0 g/10 min. This resin composition for golf balls has an improved injection-moldability and thus enables the ball to achieve both a reduced spin rate and a good durability (scuff resistance).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application Ser.No. 15/615,190 filed on Jun. 6, 2017, the entire contents of which arehereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a golf ball having a core of one or more layerand a cover of one or more layer. More particularly, the inventionrelates to a golf ball in which the core and/or cover are formed ofspecific resin compositions, thereby endowing the ball with goodproperties.

BACKGROUND ART

Golf ball resin compositions are employed particularly as cover-formingmaterials that are injection-molded over the ball core. In suchapplications, it is important to ensure that the resin composition has afluidity suitable for injection molding. One key property of the resincomposition is thus the melt flow rate (MFR). Suitable adjustment of theMFR is particularly important in cases where the cover is to be formedto a thickness (gauge) of less than 1.0 mm. When the desired MFR can beobtained, the golf ball ultimately produced often is able to achieveboth a reduced spin rate and a good durability (scuff resistance).

Various modifiers and additives are typically compounded in resincompositions for golf balls. For example, a number of disclosures relateto the use of compounds having a fluorene skeleton as additives. In onesuch disclosure, JP-A 2002-509161, a fluorene derivative is included asa visible-light initiator within a golf ball material. In addition, JP-A2013-94666 and JP-A 2013-94668 teach art that includes, within acore-forming material, an organic fluorescent material selected from agroup of compounds having fluorene skeletons.

However, the compounds with fluorene skeletons mentioned in theseprior-art publications are intended for use as visible-light initiatorsor organic fluorescent materials. They are not intended for use inadjusting the melt flow rate of resin compositions.

Also, JP No. 4514491 discloses art which, in order to reclaim plasticmaterials containing spent (used) polymer, ensures practical propertiessuch as flame retardancy and mechanical characteristics by including, asa compatibilizing agent, a compound having a fluorene skeleton.

However, the foregoing art neither teaches nor even mentions the abilityto both ensure a good fluidity and also achieve ball properties such asa reduced ball spin rate and good scuff resistance by including acompound having a fluorene skeleton within a golf ball resin material,particularly a resin composition for golf ball covers having a smallgauge.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a golf ball inwhich a specific resin composition, particularly when used as a golfball cover material, can be properly molded even if the cover gauge issmall, enabling the spin rate of the golf ball to be reduced and theball to be imparted with a good scuff resistance.

As a result of extensive investigations, we have discovered that a golfball resin composition having an improved fluidity can be obtained byadding a specific amount of (B) a fluorene skeleton-containing compoundor a derivative thereof to 100 parts by weight of (A) a thermoplasticresin. As a result, the resin material has a better injectionmoldability, which in turn makes it possible to endow the golf ball withboth a reduced spin rate and a good scuff resistance. In particular,when such a composition is used as a golf ball cover material, the covercan be properly molded even when the cover has a small gauge, thusmaking it possible to effectively impart the golf ball with a reducedspin rate and a good scuff resistance.

Accordingly the invention provides a golf ball having a core and a coverof at least one layer, wherein the outermost layer of the cover isformed of a resin composition containing (A) 100 parts by weight of athermoplastic resin, and (B) 1 to 30 parts by weight of a compoundhaving a fluorene skeleton or a derivative thereof, and the resincomposition has a melt flow rate of at least 3.0 g/10 min.

In a preferred embodiment, the thermoplastic resin (A) is at least oneresin component selected from the group consisting of:

(a-1) binary copolymers of an olefin and an α,β-unsaturated carboxylicacid of 3 to 8 carbon atoms,

(a-2) ionomer resins that are metal ion neutralization products ofbinary copolymers of an olefin and an α,β-unsaturated carboxylic acid of3 to 8 carbon atoms,

(a-3) ternary copolymers of an olefin, an α,β-unsaturated carboxylicacid of 3 to 8 carbon atoms and an α,β-unsaturated carboxylic acidester, and

(a-4) ionomer resins that are metal ion neutralization products ofternary copolymers of an olefin, an α,β-unsaturated carboxylic acid of 3to 8 carbon atoms and an α,β-unsaturated carboxylic acid ester.

In another preferred embodiment, the thermoplastic resin (A) is at leastone resin component selected from the group consisting of:

(a-2) ionomer resins that are metal ion neutralization products ofbinary copolymers of an olefin and an α,β-unsaturated carboxylic acid of3 to 8 carbon atoms, and

(a-4) ionomer resins that are metal ion neutralization products ofternary copolymers of an olefin, an α,β-unsaturated carboxylic acid of 3to 8 carbon atoms and an α,β-unsaturated carboxylic acid ester.

In this preferred embodiment, the at least one resin component has anacid content of at least 16 wt %.

In the golf ball of the invention, it is preferable for an ionomer resinhaving an acid content of at least 16 wt % to account for at least 50 wt% of component (A).

In a further preferred embodiment, the thermoplastic resin (A) is apolyamide or a polyamide elastomer.

In the inventive golf ball, the compound having a fluorene skeleton orderivative thereof serving as component (B) is preferably a bisphenol ora bisalcohol.

In the golf ball of the invention, the resin composition may furtherinclude, per 100 parts by weight of component (A):

(C) from 5 to 120 parts by weight of a fatty acid having a molecularweight of 228 to 1,500 and/or a derivative thereof, and

(D) from 0.1 to 17 parts by weight of a basic inorganic metal compoundsthat can neutralize unneutralized acid groups in components (A) and (C).

The resin composition preferably has a melt flow rate of at least 3.0g/10 min. Typically, the melt flow rate of the resin composition is atleast 1.2 times the melt flow rate of the thermoplastic resin serving ascomponent (A).

In the golf ball of the invention, the outermost layer of the coverpreferably has a gauge of from 0.1 to 1.2 mm.

In the golf ball of the invention, it is preferable that the lower limitof the content of component (B) is 10 parts by weight, per 100 parts byweight of the thermoplastic resin serving as component (A).

ADVANTAGEOUS EFECTS OF THE INVENTION

In the golf ball of the invention, the resin composition has an improvedinjection-moldability, thus enabling the ball to achieve both a reducedspin rate and a good durability (scuff resistance). When this resincomposition is used as a golf ball cover material in particular, moldingcan be properly carried out even when the cover gauge is small, enablingthe golf ball to be effectively imparted with a low spin rate and a gooddurability (scuff resistance).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The objects, features and advantages of the invention will become moreapparent from the following detailed description.

The golf ball of the invention has a core and a cover of at least onelayer. The outermost layer of the cover is formed of a resin compositioncontaining:

(A) a thermoplastic resin, and

(B) a compound having a fluorene skeleton or a derivative thereof.

Component (A) is a thermoplastic resin. Illustrative examples includeionomer resins, olefin resins, vinyl resins, polyolefin elastomers(including polyolefins and metallocene polyolefins), polystyreneelastomers, diene polymers, polyacrylate polymers, polyamide elastomers,polyurethane elastomers and polyester elastomers.

The thermoplastic resin of component (A) is preferably at least oneresin component selected from the group consisting of (a-1) to (a-4)below:

(a-1) binary copolymers of an olefin and an α,β-unsaturated carboxylicacid of 3 to 8 carbon atoms,

(a-2) ionomer resins that are metal ion neutralization products ofbinary copolymers of an olefin and an α,β-unsaturated carboxylic acid of3 to 8 carbon atoms,

(a-3) ternary copolymers of an olefin, an α,β-unsaturated carboxylicacid of 3 to 8 carbon atoms and an α,β-unsaturated carboxylic acidester, and

(a-4) ionomer resins that are metal ion neutralization products ofternary copolymers of an olefin, an α,β-unsaturated carboxylic acid of 3to 8 carbon atoms and an α,β-unsaturated carboxylic acid ester.

The olefin used in these resins (a-1) to (a-4) is preferably an olefinhaving from 2 to 6 carbon atoms, with ethylene being especiallypreferred. The unsaturated carboxylic acid used in resins (a-1) to (a-4)has from 3 to 8 carbon atoms and is exemplified by acrylic acid andmethacrylic acid. The unsaturated carboxylic acid ester used incomponent (A), although not particularly limited, is preferably a loweralkyl ester, with butyl acrylate (n-butyl acrylate, iso-butyl acrylate)being especially preferred.

The unsaturated carboxylic acid content (acid content) in resins (a-1)to (a-4) above, although not particularly limited, is preferably atleast 16 wt %, and more preferably at least 17 wt %, but preferably notmore than 21 wt %, and more preferably not more than 20 wt %. When theacid content is lower than this range, moldings of the golf ballmaterial may not have a good resilience. On the other hand, when theacid content is high, the hardness may become excessive, possiblyaffecting the durability of the ball to impact.

With a resin selected from (a-1) to (a-4) above as the base resin, theresin composition may further include: (C) a fatty acid having amolecular weight of 228 to 1,500 and/or a derivative thereof, and (D) abasic inorganic metal compound that can neutralize unneutralized acidgroups in components (A) and (C). The content of component (C) ispreferably in the range of 5 to 120 parts by weight per 100 parts byweight of component (A). The content of component (D) is preferably inthe range of 0.1 to 17 parts by weight per 100 parts by weight ofcomponent (A).

Component (C) and (D) may be, for example, the “fatty acid and/orderivative thereof” and the “basic inorganic metal compound” of theresin compositions described in JP No. 3729243.

In addition, the thermoplastic resin of component (A) is preferably apolyamide or a polyamide elastomer. In cases where a polyamide elastomeris used as component (A), illustrative examples of the polyamideelastomer include the Daiamid series (E75K2, E62K2, N1901) fromDaicel-Evonik Ltd., the Vestamid series (E58-4) from Daicel-Evonik Ltd.,and the Pebax series (Rnew 25R53, Rnew 63R53, Rnew 72R53, 2533, 6333,7233) from Arkema KK.

Component (B) is a compound having a fluorene skeleton, or a derivativethereof. Specifically, the fluorene skeleton-containing compoundsmentioned in JP No. 4514491 may be used as component (B).

The compound having a fluorene skeleton, or the derivative thereof, ispreferably a bisphenol or a bisalcohol. Illustrative examples ofcompounds having a fluorene skeleton or derivatives thereof include9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene,9,9-bis(4-hydroxyphenvl)fluorene and9,9-bis(4-hydroxy-3-methylphenyl)fluorene.

The content of component (B) is from 1 to 30 parts by weight, andpreferably from 3 to 25 parts by weight, per 100 parts by weight of thethermoplastic resin serving as component (A). When this content is toohigh, the scuff resistance worsens even though the resin composition mayhave a good fluidity. On the other hand, when this content is too low,the moldability worsens and a reduced spin rate cannot be achieved.

The combined amount of base resin consisting of components (A) and (B)is not particularly limited, although it is recommended that this be atleast 60 wt %, preferably at least 70 wt %, more preferably at least 80wt %, and most preferably at least 90 wt %, of the total amount of theresin composition. When this content is inadequate, the desired effectsof the invention may not be obtained.

In addition, optional additives may be suitably included within theresin composition according to the intended use of the composition. Forexample, when the resin composition for golf balls of the invention isto be used as a cover material, various types of additives, such asfillers (inorganic fillers), organic staple fibers, reinforcing agents,crosslinking agents, colorants, dispersants, antioxidants, ultravioletabsorbers and light stabilizers, may be added to the foregoingingredients. When such additives are included, the content thereof, per100 parts by weight of the base resins, is preferably at least 0.1 partby weight, and more preferably at least 0.5 part by weight, butpreferably not more than 10 parts by weight, and more preferably notmore than 4 parts by weight.

The resin composition can be obtained by mixing the above ingredientsusing any of various types of mixers, such as a kneading-typesingle-screw or twin-screw extruder, a Banbury mixer, a kneader or aLabo Plastomill.

The resin composition has a melt flow rate (MFR) of at least 3.0 g/10min, and preferably at least 3.5 g/10 min. MFR refers here to the meltflow rate measured at a test temperature of 190° C. and under a testload of 21.18 N (2.16 kgf) in accordance with JIS-K7210. At an MFR inthis range, a fluidity that is particularly suitable for injectionmolding can be ensured, improving the moldability and making it possiblefor the golf balls that are ultimately manufactured to have both areduced spin rate and a good durability (scuff resistance).

In order for the resin composition to have an improved injectionmoldability and to fully manifest in the golf ball the desired effect ofbeing able to achieve both a reduced spin rate and a good durability(scuff resistance), it is preferable for the resin composition to havean MFR value which is at least 1.2 times, and preferably at least 1.3times, and more preferably at least 1.5 times, the MFR of thethermoplastic resin serving as component (A).

The resin composition can be used as the cover material in a two-piecesolid golf ball consisting of a core and a cover that encases the core,or in a multi-piece solid golf ball consisting of a core of at least onelayer and a multilayer cover encasing the core.

The core can be formed using a known rubber material as the basematerial. Known base rubbers such as natural rubbers or syntheticrubbers may be used as the base rubber. More specifically, the use ofprimarily a polybutadiene, especially cis-1,4-polybutadiene having a cisstructure content of at least 40%, is recommended. Within the baserubber, where desired, natural rubber, polyisoprene rubber,styrene-butadiene rubber or the like may be used together with the abovepolybutadiene.

The polybutadiene may be synthesized using a neodymium catalyst or otherrare-earth catalyst, or a metal catalyst such as a cobalt catalyst ornickel catalyst.

Co-crosslinking agents such as unsaturated carboxylic acids and metalsalts thereof, inorganic fillers such as zinc oxide, barium sulfate andpotassium carbonate, and organic peroxides such as dicumyl peroxide and1,1,-bis(t-butylperoxy)cyclohexane may be included in the above baserubber. Where necessary, a commercial antioxidant may also be suitablyadded.

The core has a diameter which, although not particularly limited, ispreferably at least 20 mm, more preferably at least 25 mm and even morepreferably at least 30 mm. The upper limit is preferably not more than41 mm, and more preferably not more than 40 mm.

The core deflection, which is the amount of deformation by the core whencompressed under a final load of 1,275 N (130 kgf) from an initial loadof 98 N (10 kgf), is preferably at least 2.0 mm, more preferably atleast 2.5 mm, and even more preferably at least 3.0 mm. The upper limitis preferably not more than 6.0 mm, and more preferably not more than5.0 mm. When the amount of deformation is too small, the feel of theball at impact may be too hard. On the other hand, when the amount ofdeformation is too large, the feel at impact may be too soft or thedurability of the ball to cracking when repeatedly struck may worsen.

The cover is formed of at least one layer. When the cover consists of aplurality of layers, in addition to an outermost laver, it includes alsoat least an intermediate layer interposed between the outermost layerand the core. Accordingly, the cover may be a two-layer cover consistingof, in order from the inside: an intermediate layer and an outermostlayer. In addition, an envelope laver may be provided between the coreand the intermediate layer. In this case, the cover may be a three-layercover consisting of, in order from the inside: an envelope layer, anintermediate layer and an outermost layer.

Each layer of the cover has a gauge which, although not particularlylimited, is preferably at least 0.1 mm, more preferably at least 0.3 mm,and even more preferably at least 0.5 mm. The upper limit is preferablynot more than 1.2 mm, more preferably not more than 1.1 mm, and evenmore preferably not more than 1.0 mm.

Each layer of the cover has a Shore D hardness which, although notparticularly limited, is preferably at least 30, and more preferably atleast 40. The upper limit is preferably not more than 75, morepreferably not more than 70, and even more preferably not more than 65.

The ball deflection, which is the amount of deformation by the ball whencompressed under a final load of 1,275 N (130 kgf) from an initial loadof 98 N (10 kgf), is preferably at least 2.0 mm, and more preferably atleast 2.5 mm. The upper limit is preferably not more than 4.0 mm, andmore preferably not more than 3.8 mm. When the amount of deformation istoo small, the feel of the ball at impact may be too hard. On the otherhand, when the amount of deformation is too large, the feel at impactmay be too soft or the durability of the ball to cracking whenrepeatedly struck may worsen.

Numerous dimples of one, two or more types may be formed on the surfaceof the cover. In addition, various types of coatings may be applied tothe cover surface. Given the need for the golf ball to withstand harshconditions of use, preferred examples of such coatings include two-partcuring urethane coatings, especially non-yellowing urethane coatings.

EXAMPLES

Working Examples and Comparative Examples are provided below toillustrate the invention, and are not intended to limit the scopethereof.

Working Examples 1 to 7. Comparative Examples 1 to 7

Solid cores were produced by using the two types of rubber compositionsI and II shown in Table 1 below and vulcanizing for 15 minutes at 155°C.

TABLE 1 Rubber formulations (pbw) I II BR01 80 80 BR51 20 20 Bariumsulfate 26.8 25.6 Zinc white 4.0 4.0 Zinc stearate 5.0 5.0 Nocrac NS-60.1 0.1 Zinc salt of pentachlorothiophenol 1.0 1.0 Zinc acrylate (ZDA)23.0 26.0 Percumyl D 0.6 0.6 Perhexa C40 1.2 1.2

Details on the above core formulations I and II are given below.

-   BR01: cis-1,4-Polybutadiene rubber available under this trade name    from JSR Corporation.-   BR51: cis-1,4-Polybutadiene rubber available under this trade name    from JSR Corporation.-   Barium sulfate: Available from Sakai Chemical Co., Ltd.-   Zinc white (zinc oxide):    -   Available from Sakai Chemical Co., Ltd.-   Zinc stearate: Available from Wako Pure Chemical Industries, Ltd.-   Nocrac NS-6: 2,2′-Methylenebis(4-methyl-6-t-butylphenol) available    under this trade name from Ouchi Shinko Chemical Industry Co., Ltd.-   Zinc salt of pentachlorothiophenol:    -   Available from Wako Pure Chemical Industries, Ltd.-   Zinc acrylate: Available from Wako Pure Chemical Industries, Ltd.-   Percumyl D: Dicumyl peroxide available under this trade name from    NOF Corporation-   Perhexa C-40: A mixture of 1,1-di(tert-butylperoxy)cyclohexane and    silica available under this trade name from NOF Corporation.

Next, in Working Examples 1 to 7 and Comparative Examples 1 to 7, first,the resin indicated as “A” in Table 2 below was injected into a mold inwhich the solid core had been placed, thereby giving a sphere consistingof the solid core encased by an intermediate layer having a gauge of1.45 mm. Next, in the respective Examples, one of the resin compositionsindicated as “B” to “K” in Table 2 below was mixed and extruded with akneading-type twin-screw extruder to give a pelletized resincomposition, which was then injected into a mold in which the sphere hadbeen placed, thus forming an outermost layer having a gauge of 1.00 mmor 1.25 mm and producing a three-piece solid golf ball. Dimples commonto all the Examples were formed on the surface of the cover.

TABLE 2 Resin composition (pbw) A B C D E F G H I J K HPF 1000 100 Baseresin Himilan AM 7318 75 75 75 75 75 75 50 50 25 25 Himilan AM 7327 2525 25 25 25 25 50 50 75 75 Fluorene MF-11 3 5 10 20 40 10 10 PhysicalShore D hardness 51 62 63 63 63 64 65 57 58 52 53 properties MFR (g/10min) 0.65 2.2 3.3 3.5 4.3 5.1 6.2 2.3 4.4 2.5 4.6 MFR ratio — 1.0 1.51.6 2.0 2.3 2.8 1.0 1.9 1.0 1.8 *In the table, “MFR ratio” = MFR ofresin composition/MFR of base resin.

Details on the materials mentioned in Table 2 are given below.

-   HPF 1000: HPF™ 1000, available from E.I. DuPont de Nemours & Co.,    Ltd.-   Himilan AM 7318: A sodium-neutralized ionomer available from    DuPont-Mitsui Polychemicals Co., Ltd.: acid content, 18 wt %; MFR,    2.2 g/10 min-   Himilan AM 7327: A zinc-neutralized ionomer available from    DuPont-Mitsui Polychemicals Co., Ltd.; acid content, 9 wt %: MFR,    2.5 g/10 min-   Fluorene MF-11: A compound having a fluorene skeleton, available    from Osaka Gas Chemicals Co., Ltd.    Shore D Hardness of Cover Material

The cover material (resin composition) was molded into a sheet having athickness of 2 mm and left to stand for at least two weeks, followingwhich the Shore D hardness was measured in accordance with ASTMD2240-95.

MFR (g/10 Min) of Cover Resin Composition

The melt flow rate was measured at a test temperature of 190° C. andunder a test load of 21.18 N (2.16 kgf) in accordance with JIS-K7210.

Using the methods described below, the core and ball diameter anddeflection were measured for each of the golf balls thus obtained, inaddition to which the spin rate-lowering properties, scuff resistanceand moldability of the ball were evaluated.

Core and Golf Ball Diameter

The diameters at five random dimple-free areas on the surface of a ballwere measured at a temperature of 23.9±1° C. and, using the average ofthese measurements as the measured value for a single ball, the averagediameter for five measured balls was determined. The diameters of thecores were measured in the same way.

Golf Ball Deflection

The golf ball was placed on a hard plate and the amount of deflectionwhen compressed under a final load of 1,275 N (130 kgf) from an initialload of 98 N (10 kgf) was measured. The amount of deflection here refersin each case to the measured value obtained after holding the ballisothermally at 23.9° C.

Moldability

The injection moldability of each golf ball was rated as follows.

-   -   Good: Molding can be carried out without difficulty.    -   NG: The cover material cannot be molded, or stable molding is        impossible, resulting in eccentricity or the like.        Spin Rate of Ball (Rpm)

The ball was struck at a head speed (HS) of 45 ms with a club mounted ona swing robot, immediately after which the backspin rate of the ball wasmeasured with an apparatus for measuring initial conditions.

Scuff Resistance

The golf balls were held isothermally at 23° C. and five balls of eachtype were hit at a head speed of 33 m/s using as the club a pitchingwedge mounted on a swing robot machine. The damage to the ball from theimpact was visually rated according to the following criteria. Theaverage rating for each type of ball is indicated in the table.

Exc: No damage or substantially no damage.

Good: Damage is apparent but so slight as to be of substantially noconcern.

NG: Some fraying of surface or loss of dimples.

TABLE 3 Working Example 1 2 3 4 5 6 7 Core Material I I I II I I IDiameter (mm) 37.8 37.8 37.8 37.8 37.8 37.8 37.8 Intermediate layerMaterial A A A A A A A Gauge (mm) 1.45 1.45 1.45 1.45 1.45 1.45 1.45Outermost layer Material C D E E F I K Gauge (mm) 1.00 1.00 1.00 1.001.00 1.00 1.00 Finished ball Diameter (mm) 42.7 42.7 42.7 42.7 42.7 42.742.7 Deflection (mm) 3.2 3.2 3.2 2.9 3.1 3.3 3.4 Performance testsMoldability Good Good Good Good Good Good Good Spin rate (rpm), W#12,570 2,560 2,560 2,640 2,560 2,600 2,640 Scuff resistance Exc Exc ExcExc Good Good Good

TABLE 4 Comparative Example 1 2 3 4 5 6 7 Core Material I I I I I II IDiameter (mm) 37.3 37.8 37.8 37.8 37.3 37.3 37.3 Intermediate layerMaterial A A A A A A A Gauge (mm) 1.45 1.45 1.45 1.45 1.45 1.45 1.45Outermost layer Material B B G H H H J Gauge (mm) 1.25 1.00 1.00 1.001.25 1.25 1.25 Finished ball Diameter (mm) 42.7 42.7 42.7 42.7 42.7 42.742.7 Deflection (mm) 3.2 — 3.0 — 3.3 3.0 3.4 Performance testsMoldability Good NG Good NG Good Good Good Spin rate (rpm), W#1 2,610 —2,560 — 2,660 2,750 2,700 Scuff resistance Exc — NG — Good Good Good

From Tables 3 and 4, it is apparent that the golf balls in ComparativeExamples had the following drawbacks.

In Comparative Example 1, although molding was carried out to a covergauge at which stable molding is possible, compared with WorkingExamples 1 to 3 and 5 in which the same base resin formulations wereused in the cover, the spin rate of the ball on shots with a driver(W#1) was somewhat high.

In Comparative Example 2, the resin composition had a low melt flowrate, as a result of which the ball could not be stably molded.

In Comparative Example 3, the amount of compound having a fluoreneskeleton added was high, resulting in a poor scuff resistance.

In Comparative Example 4, the melt flow rate of the resin compositionwas low, as a result of which the ball could not be stably molded.

In Comparative Example 5, although molding was carried out to a covergauge at which stable molding is possible, compared with Working Example6 in which the same base resin formulations were used in the cover, thespin rate of the ball when hit with a driver (W#1) was high.

In Comparative Example 6, although molding was carried out to a covergauge at which stable molding is possible, the spin rate of the ball onshots with a driver (W#1) was high.

In Comparative Example 7, although molding was carried out to a covergauge at which stable molding is possible, compared with Working Example7 in which the same base resin formulations were used in the cover, thespin rate of the ball when hit with a driver (W#1) was high.

Working Examples 8 to 15, Comparative Examples 8 & 9

Solid cores were produced by using a rubber compositions III shown inTable 5 below and vulcanizing for 15 minutes at 155° C.

TABLE 5 Rubber formulations (pbw) III BR01 80 BR51 20 Barium sulfate22.0 Zinc white 4.0 Zinc stearate 5.0 Nocrac NS-6 0.1 Zinc salt ofpentachlorothiophenol 1.0 Zinc acrylate (ZDA) 23.0 Percumyl D 0.6Perhexa C40 1.2

Details on the above core formulation III are the same as the abovedescription of core formulations I and II.

Next, in Working Examples 8 to 15 and Comparative Examples 8 & 9, first,the resin indicated as “A” in Table 6 below was injected into a mold inwhich the solid core had been placed, thereby giving a sphere consistingof the solid core encased by an intermediate layer having a gauge of1.45 mm. Next, in the respective Examples, one of the resin compositionsindicated as “PA1” to “PA10” in Table 6 below was mixed and extrudedwith a kneading-type twin-screw extruder to give a pelletized resincomposition, which was then injected into a mold in which the sphere hadbeen placed, thus forming an outermost layer having a gauge of 1.00 mmand producing a three-piece solid golf ball. Dimples common to all theExamples were formed on the surface of the cover.

TABLE 6 Resin composition (pbw) PA1 PA2 PA3 PA4 PA5 PA6 PA7 PA8 PA9 PA10Base resin Vestamid E58K 50 50 50 50 50 Daiamid E62K2 40 40 40 40 40Daiamid E57K2 50 50 50 50 50 Daiamid N1901 60 60 60 60 60 Fluorene MF-113 5 10 20 3 5 10 20 Physical Shore D hardness 68 70 70 70 70 68 70 70 7070 properties MFR (g/10 min) 6.5 8.3 9.1 11.2 15.3 7.0 7.7 8.1 9.1 11.4MFR ratio — 1.1 1.3 1.6 2.2 — 1.1 1.2 1.3 1.6 *In the table, “MFR ratio”= MFR of resin composition/MFR of base resin.

Details on the materials mentioned in Table 6 are given below.

Vestamid E58K: A polyamide elastomer available from Daicel-Evonik Ltd.

Daiamid E62K2. E75K2, N1901: A polyamide elastomer available fromDaicel-Evonik Ltd.

Fluorene MF-11: A compound having a fluorene skeleton, available fromOsaka Gas Chemicals Co., Ltd.

Shore D Hardness of Cover Material

The cover material (resin composition) was molded into a sheet having athickness of 2 mm and left to stand for at least two weeks, followingwhich the Shore D hardness was measured in accordance with ASTMD2240-95.

MFR (g/10 Min) of Cover Resin Composition

The melt flow rate was measured at a test temperature of 190° C. andunder a test load of 21.18 N (2.16 kgf) in accordance with JIS-K7210.

Using the methods described below, the core and ball diameter anddeflection were measured for each of the golf balls thus obtained, inaddition to which the spin rate-lowering properties, scuff resistanceand moldability of the ball were evaluated.

Core and Golf Ball Diameter

The diameters at five random dimple-free areas on the surface of a ballwere measured at a temperature of 23.9±1° C. and, using the average ofthese measurements as the measured value for a single ball, the averagediameter for five measured balls was determined. The diameters of thecores were measured in the same way.

Golf Ball Deflection

The golf ball was placed on a hard plate and the amount of deflectionwhen compressed under a final load of 1,275 N (130 kgf) from an initialload of 98 N (10 kgf) was measured. The amount of deflection here refersin each case to the measured value obtained after holding the ballisothermally at 23.9° C.

Moldability

The injection moldability of each golf ball was rated as follows.

Good: Molding can be carried out without difficulty.

NG: The cover material cannot be molded, or stable molding isimpossible, resulting in eccentricity or the like.

Spin Rate of Ball (rpm)

The ball was struck at a head speed (HS) of 45 m/s with a club mountedon a swing robot, immediately after which the backspin rate of the ballwas measured with an apparatus for measuring initial conditions.

Scuff Resistance

The golf balls were held isothermally at 23° C. and five balls of eachtype were hit at a head speed of 33 m/s using as the club a pitchingwedge mounted on a swing robot machine. The damage to the ball from theimpact was visually rated according to the following criteria. Theaverage rating for each type of ball is indicated in the table.

Exc: No damage or substantially no damage.

Good: Damage is apparent but so slight as to be of substantially noconcern.

NG: Some fraying of surface or loss of dimples.

TABLE 7 Working Example Working Example C. E. 8 8 9 10 11 C. E. 9 12 1314 15 Core Material III III III III III III III III III III Diameter(mm) 37.8 37.8 37.8 37.8 37.8 37.8 37.8 37.8 37.8 37.8 IntermediateMaterial A A A A A A A A A A layer Gauge (mm) 1.45 1.45 1.45 1.45 1.451.45 1.45 1.45 1.45 1.45 Outermost Material PA1 PA2 PA3 PA4 PA5 PA6 PA7PA8 PA9 PA10 layer Gauge (mm) 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.001.00 1.00 Finished ball Diameter (mm) 42.7 42.7 42.7 42.7 42.7 42.7 42.742.7 42.7 42.7 Deflection 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 (mm)Performance Moldability Good Good Good Good Good Good Good Good GoodGood tests Spin rate 2,560 2,416 2,413 2,426 2,425 2,560 2,413 2,4142,427 2,429 (rpm), W#1 Scuff resistance NG Good Good Good Good NG GoodGood Good Good *it is noted that “C. E. 8” and “C. E. 9” means“Comparative Example 8” and “Comparative Example 9”, respectively.

From Table 7, it is apparent that the golf balls in Comparative Exampleshad the following drawbacks.

In Comparative Example 8, compared with Working Examples 8-11 in whichthe same base resin formulations were used in the cover, the spin rateof the ball when hit with a driver (W#1) was somewhat high and the scuffresistance of the ball was poor.

In Comparative Example 9, compared with Working Examples 12-15 in whichthe same base resin formulations were used in the cover, the spin rateof the ball when hit with a driver (W#1) was somewhat high and the scuffresistance of the ball was poor.

Japanese Patent Application No. 2016-124406 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A golf ball comprising a core and a coverof at least one layer, wherein the outermost layer of the cover isformed of a resin composition comprising: (A) 100 parts by weight of athermoplastic resin, and (B) 1 to 30 parts by weight of a compoundhaving a fluorene skeleton or a derivative thereof, wherein the resincomposition has a melt flow rate of at least 3.0 g/10 min.
 2. The golfball of claim 1, wherein the thermoplastic resin (A) is at least oneresin component selected from the group consisting of: (a-1) binarycopolymers of an olefin and an α,β-unsaturated carboxylic acid of 3 to 8carbon atoms, (a-2) ionomer resins that are metal ion neutralizationproducts of binary copolymers of an olefin and an α,β-unsaturatedcarboxylic acid of 3 to 8 carbon atoms, (a-3) ternary copolymers of anolefin, an α,β-unsaturated carboxylic acid of 3 to 8 carbon atoms and anα,β-unsaturated carboxylic acid ester, and (a-4) ionomer resins that aremetal ion neutralization products of ternary copolymers of an olefin, anα,β-unsaturated carboxylic acid of 3 to 8 carbon atoms and anα,β-unsaturated carboxylic acid ester.
 3. The golf ball of claim 1,wherein the thermoplastic resin (A) is at least one resin componentselected from the group consisting of: (a-2) ionomer resins that aremetal ion neutralization products of binary copolymers of an olefin andan α,β-unsaturated carboxylic acid of 3 to 8 carbon atoms, and (a-4)ionomer resins that are metal ion neutralization products of ternarycopolymers of an olefin, an α,β-unsaturated carboxylic acid of 3 to 8carbon atoms and an α,β-unsaturated carboxylic acid ester; and said atleast one resin component has an acid content of at least 16 wt %. 4.The golf ball of claim 1, wherein an ionomer resin having an acidcontent of at least 16 wt % accounts for at least 50 wt % of component(A).
 5. The golf ball of claim 1, wherein said compound having afluorene skeleton or derivative thereof serving as component (B) is abisphenol or a bisalcohol.
 6. The golf ball of claim 1, wherein theresin composition further comprises, per 100 parts by weight ofcomponent (A): (C) from 5 to 120 parts by weight of a fatty acid havinga molecular weight of 228 to 1,500 or a derivative thereof or both, and(D) from 0.1 to 17 parts by weight of a basic inorganic metal compoundthat can neutralize unneutralized acid groups in components (A) and (C).7. The golf ball of claim 1, wherein the melt flow rate of the resincomposition is at least 1.2 times the melt flow rate of thethermoplastic resin serving as component (A).
 8. The golf ball of claim1, wherein the outermost layer of the cover has a gauge of from 0.1 to1.2 mm.
 9. The golf ball of claim 1, wherein the lower limit of thecontent of component (B) is 10 parts by weight, per 100 parts by weightof the thermoplastic resin serving as component (A).
 10. The golf ballof claim 1, wherein the thermoplastic resin (A) is a polyamide or apolyamide elastomer.